Fixed multifunction probe for aircraft

ABSTRACT

A fixed multifunction probe, e.g., for aircraft and configured to measure air flow parameters near an airplane. The probe includes a body closed by a rounded cap, at least three pressure taps situated at specified positions of the body, a pressure measurement mechanism for measuring at least as many pressures as pressure taps, and a calculation device for calculating the air flow parameters.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multifunction probe intended formeasuring the static and total pressures, as well as the angle of attackof the flow of a fluid near an aircraft. The probe is especiallyintended for measuring the flow parameters of the air near an airplane.

2. Discussion of the Background

The static pressure is a very important parameter for the safety of anairplane. An international standard establishes a correspondence betweenthe static pressure and the altitude. This correspondence is used toassociate an aircraft with an altitude in a unique manner by allocatingit a static pressure value to be complied with during the flightthereof.

The total pressure is not utilized as it stands, but it makes itpossible to determine the dynamic pressure by calculating thedifferential pressure between the total pressure and the staticpressure. The dynamic pressure is a very important parameter since itmakes it possible to determine the velocity of the air flow; thevelocity of the air flow coming into play, for its part, in calculatingthe lift of the airplane.

The pressure measurements are performed by way of pressure taps. Thefirst known probes were equipped with a single pressure tap. Thislimitation compelled the use of several probes in order to be able toperform the various pressure measurements.

The configuration customarily adopted comprises:

a static pressure probe for measuring the local static pressure Ps

a total pressure probe for measuring the total pressure Pt

and a vane for measuring the local angle of attack α.

With such a configuration, the calculation of the parameters, staticpressure Ps, total pressure Pt and local angle of attack α, requires theaccurate knowledge on the one hand of the characteristics of the threeprobes, and on the other hand of the aerodynamic field of the airplaneat the points of position of the probes on the fuselage. Furthermore,each probe requires its de-icing system.

To remedy these drawbacks, the person skilled in the art may resort to amultifunction probe. A multifunction probe advantageously makes itpossible to measure the above parameters at one and the same point ofthe airplane. Optimization of the position of the probe eases thecalculations. The use of a multifunction probe makes it possible toreduce the number of probes, and consequently, it makes it possible toreduce the heating power required for de-icing. There are various typesof multifunction probe.

A first type encompasses moveable multifunction probes. A probe of thistype comprises a moveable part, generally referred to as the vane, whichpositions itself in the direction of the air stream and which carriesstatic and total pressure taps. The manufacture of probes of this typepresents significant difficulties. The vane compels a complex mechanicallink with the fixed part of the probe. The link must allow rotation ofthe vane while ensuring continuity of the pressure ducts between thevane and the fixed part, while this continuity must not exhibit anyleaks. Sealing is therefore difficult to achieve since it must becompatible with the rotation of the vane.

A second type encompasses fixed multifunction probes. A typical probe isdescribed in the patent U.S. Pat. No. 4,096,744. This probe comprisespressure taps distributed at various locations of the probe. Thisdistribution gives the possibility, after calculation, of accessing thealtitude, velocity and angle of attack information. However, this probecomprises a total pressure tap Pt at the front extremity of the probe;this tap is often referred to by the name “Pitot”. The Pitot tap rendersthe nose of the probe fragile. U.S. Pat. No. 5,628,565 describes anelaborate probe which is capable, simultaneously, of measuring variouspressures and of measuring the temperature of the air stream. However,this probe is also equipped with a Pitot tap which renders the nose ofthe probe fragile.

An aim of the invention is to provide a fixed multifunction probe foraircraft which does not have the drawback recalled above.

BRIEF SUMMARY OF THE INVENTION

Accordingly, the subject of the invention is a fixed multifunction probefor aircraft having a closed front part and having at least threepressure taps distributed in various sections at specified points of thebody of the probe. The fixed multifunction probe according to theinvention makes it possible to measure the flow parameters of the fluidmoving with respect to the probe. To this end, it comprises:

a body having symmetry of revolution about a longitudinal axis, closedby a rounded cap, the body being placed in the flow,

at least three pressure taps situated at specified points of the bodyand distributed in various sections so as to tap a first pressure, asecond pressure and a third pressure,

pressure measurement means associated with the pressure taps formeasuring at least as many pressures P1, . . . , Pn as pressure taps,

calculation means for calculating the local angle of attack α of theflow by expressing a specified ratio of measured pressures as a functionof the local angle of attack a in the form:$\frac{{P1} - {P2}}{{P1} + {P2}} = \frac{A + {{B \cdot \cos}\quad 2\quad \alpha} + {{C \cdot \sin}\quad 2\quad \alpha}}{D + {{E \cdot \cos}\quad 2\quad \alpha} + {{F \cdot \sin}\quad 2\alpha}}$

A, B, C, D, E, F being constants dependent solely on the coordinates ofthe pressure taps, the specified position of the pressure taps beingsuch that the expression for the ratio as a function of the local angleof attack α is quasi linear,

and for calculating the total pressure Pt of the flow at the level ofthe probe, the static pressure at upstream infinity of the probe Ps_(∞)and the dynamic pressure Pt−Ps_(∞) from the pressure coefficients kP ofthe pressure taps.

By virtue of the absence of any Pitot pressure tap, a probe according tothe invention is more robust than a fixed multifunction probe equippedwith such a tap. Furthermore, the absence of a Pitot tap makes itpossible to free up some room for installing a heating circuit, therebymaking it possible to improve the de-icing of the extremity of theprobe.

The fixed structure of the probe eases the inspection of the integrityof the probe before flight as well as the transmission of the heatingenergy and the pneumatic pressures. The structure of the probe allowsinstallation at the nose of the airplane, in a similar manner to theinstallation of a nose boom, and also installation along the fuselage,by way of a mast acting as support and by way of a fixing pad.

According to a first embodiment of the invention, the probe comprisesthree pressure taps. The pressure taps are associated with pressuremeasurement means and with calculation means. The probe makes itpossible to retrieve the local angle of attack, the total pressure andthe static pressure of the aerodynamic flow in which it is placed.Advantageously the probe comprises no total pressure tap.

According to a second embodiment of the invention, the probe comprises afourth pressure tap associated with pressure measurement means. Such aprobe also makes it possible to retrieve the parameters listed above(local angle of attack, total pressure and static pressure of the flow),but with a securing of the information which the first embodiment doesnot allow. A fault with one of the pressure taps, or with one of thepressure measurement means, may be detected and signaled on completionof a comparison between the various values calculated from the variousmeasurements. As in the first embodiment, the probe comprises no totalpressure tap.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention will be well understood and its advantages and othercharacteristics will emerge from the following description presented byway of non-limiting illustration. The description is given inconjunction with the appended figures which represent:

FIG. 1, a schematic representation of a fixed multifunction probeaccording to the invention,

FIG. 2, a schematic representation of the arrangement of the pressuretaps of a probe according to the invention,

FIG. 3, the components of the velocity of the flow at a point of theprobe,

FIG. 4, a particular arrangement of the pressure taps of the firstembodiment of a probe according to the invention,

FIG. 5, a particular arrangement of the pressure taps of the secondembodiment of a probe according to the invention,

FIG. 6, a fixed multifunction probe according to the inventionfurthermore -comprising means for measuring the total temperature.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 schematically represents a fixed multifunction probe according tothe invention. The probe comprises a body 1, pressure taps 2, pressuremeasurement means 3 and calculation means 4.

The body 1 exhibits a profile having a symmetry of revolution about alongitudinal axis X. The profile is such that the fluid flow exhibits noseparation within the useful range of angle of attack. This range mayextend for example between ±40° of angle of attack. The body is closedby a rounded cap 5. The body is placed in the fluid flow. The probecomprises at least three pressure taps 2, each pressure tap tapping apressure Pe, Pi, Pr. The pressure taps are arranged on the body andcommunicate via hermetic ducts with pressure measurement means 3. Thepressure measurement means are associated with the pressure taps 2 so asto measure at least as many pressures as pressure taps 2. The pressuremeasurement means consist of differential or absolute pressure sensorsC1, . . . , Cn. The outputs P1, . . . , Pn of the sensors are utilizedby the calculation means 4. The calculation means 4 can comprise aprocessor, or a microcontroller, for performing the calculations of thefluid flow parameters, from the measured pressure values P1, . . . , Pn.

FIG. 2 schematically represents, in a diagram, the arrangement of thepressure taps on the body 1 of a probe according to the invention. Theprobe comprises at least three pressure taps PPe, PPi, PPr such that:

PPe is characterized by its abscissa x_(e) and its angle φ_(e)

PPi is characterized by its abscissa x_(i) and its angle φ_(i)

PPr is characterized by its abscissa x_(r) and its angle φ_(r)

Each pressure tap has a pressure coefficient kP which is expressedaccording to the relations: $\begin{matrix}{{kP} = \frac{{P - {Ps}_{\infty}}\quad}{{Pt} - {Ps}_{\infty}}} & (1)\end{matrix}$

 kP=1−V ²  (2)

With:

Ps_(∞) the static pressure at upstream infinity of the probe,

P the pressure at the relevant tap,

Pt the total pressure of the flow at the level of the probe,

V the velocity of the flow at the level of the relevant tap for avelocity at upstream infinity of the probe equal to unity.

For a relevant pressure tap, the components of the velocity of the fluidflow are represented in FIG. 3. V is the fluid flow velocity at thelevel of the relevant pressure tap 6 for a velocity at upstream infinityequal to unity. The illustration represents a probe, the profile ofwhose body 1 is simulated by an ellipse. The abscissa axis X correspondsto the longitudinal axis of the probe. The fluid flow, of velocity{right arrow over (V)} and angle of attack α, can be decomposed into twoflows, a longitudinal flow and a transverse flow. To the longitudinalflow there corresponds an upstream velocity parallel to the axis ofsymmetry X of the probe and of modulus V cos α. The induced velocity{right arrow over (V)}1 cos α, at the relevant point of the surface, istangential to the meridian at this point. To the transverse flow therecorresponds an upstream velocity perpendicular to the axis of symmetry Xof the probe and of modulus V sin α. The velocity induced at therelevant point of the surface has a component, of modulus V2 sin αcos φ,tangential to the meridian at this point, and a component, of modulus V3sin αsin φ, tangential to the circle at the relevant point. φ representsthe angular position of the point with respect to the attack planedefined by the axis of symmetry X of the probe and the upstream velocity{right arrow over (V)} of the fluid flow. The values V1, V2 and V3depend solely on the abscissa of the relevant point. The superpositionof the longitudinal and transverse flows allows calculation of thevelocity V at every point of the probe, in particular at a pressure tap,according to the relation:

V ²=(V 1 cos α+V 2 sin αcos φ)²+(V 3 sin αsin φ)²  (3)

with:

α the angle of attack of the flow,

φ the angular position of the pressure tap with respect to the attackplane,

V1, V2, V3 the components of the velocity at the relevant point, thevelocities V1, V2 and V3 are calculated for an upstream infinityvelocity equal to unity. The components of the velocity V1, V2, V3depend only on the abscissa of the pressure tap. They are calculatedaccording to a customary method from the profile of the probe, forexample according to the Hess and Smith method.

The expression (2) for the pressure coefficient can be expanded usingthe formulae: cos²α=½(1+cos 2α), sin²α=½(1−cos 2α) and 2 sin α. cosα=sin 2α so as to express the coefficient in the following form:

kP=1−a−b. cos 2α−c. sin 2α  (4)

a, b and c being constants which depend only on the position of thepressure tap and the profile of the probe.

The pressure measurement means associated with the pressure taps measureat least as many pressures as pressure taps. A first means is adifferential sensor which measures P1=Pe−Pr. A second means is adifferential sensor which measures P2=Pi−Pr. A third means is anabsolute sensor which measures P3=Pr. This enables the calculation meansto calculate the ratio $\frac{{P1} - {P2}}{{P1} + {P2}}$

which can be expressed in the following forms: $\begin{matrix}{\frac{{P1} - {P2}}{{P1} + {P2}} = \frac{\left( {{Pe} - \Pr} \right) - \left( {{Pi} - \Pr} \right)}{\left( {{Pe} - \Pr} \right) + \left( {{Pi} - \Pr} \right)}} & (5) \\{\frac{{P1} - {P2}}{{P1} + {P2}} = \frac{{kPe} - {kPi}}{{kPe} + {kPi} - {2 \cdot {kPr}}}} & (6)\end{matrix}$

This ratio can be written in the form: $\begin{matrix}{\frac{{P1} - {P2}}{{P1} + {P2}} = \frac{A + {{B \cdot \cos}\quad 2\alpha} + {{C \cdot \sin}\quad 2\alpha}}{D + {{E \cdot \cos}\quad 2\alpha} + {{F \cdot \sin}\quad 2\alpha}}} & (7)\end{matrix}$

With A, B, C, D, E, F being values dependent solely on the coordinates(X_(e), X_(i), X_(n), φ_(e), φ_(i), φ_(r)) of the pressure

taps. By suitably choosing these coordinates, it is possible to contrivematters such that A=0, B=0 and F=0 and that E/D has a value such thatthe ratio $\frac{{P1} - {P2}}{{P1} + {P2}}$

is quasi linear with the angle of attack a. For example, for a variationof α of ±400, if E/D=0.560825 then the expression for the ratio as afunction of α is linear to within 10⁻³.

The calculation of the ratio $\frac{{P1} - {P2}}{{P1} + {P2}}$

thus makes it possible to determine the angle of attack α, followed bythe pressure coefficients kPe, kPi, kPr, followed by (Pt−Ps_(∞)), Ps_(∞)and Pt.

The system is not however optimized, since the variation in the ratio$\frac{{P1} - {P2}}{{P1} + {P2}}$

referred to the useful range of angle of attack a is not as large aspossible. Now, this is desirable in order to optimize the accuracy ofthe calculations.

FIG. 4 schematically represents, in a diagram, a -particular arrangementof the pressure taps of the first embodiment of a probe according to theinvention. This arrangement allows optimization of the determination ofthe flow parameters. The position of each of the three pressure taps,PPe, PPi and PPr1, is determined as a function of the profile of thebody 1 of the probe in such a way that:

PPe is situated on the extrados of the probe, in a first section 7,preferably perpendicular to the axis of the probe, and in the attackplane

PPi is situated on the intrados of the probe, in the same section as PPeand diametrically opposite PPe in the attack plane and

the tap PPr1 consists of a ring of intercommunicating holes. The ring issituated in one and the same section 8 preferably perpendicular to theaxis of the probe. The holes are preferably regularly spaced over thecircumference of this section. When the pressure tap PPr1 compriseseight holes, the latter are preferably positioned at 45° to one another.This particular embodiment corresponds to the illustration of FIG. 4.

The terms extrados and intrados make reference to an installation of theprobe along the fuselage. A pressure tap PPe is said to be situated onthe extrados of the probe when it lies in the attack plane defined bythe axis of the probe and the upstream infinity velocity of the flow,and on the side away from the wind for positive angles of attack. Anintrados tap PPi is diametrically opposite an extrados tap.

The extrados pressure taps are characterized by an angle Φ equal to 0.The intrados pressure taps are characterized by an angle Φ equal to π.

In the case of installation on the nose of the airplane, two additionalpressure taps may be arranged in the first section in a planeperpendicular to the plane containing the intrados and extrados taps.The four pressure taps of the first section are preferably equidistantfrom one another.

By knowing the components of the velocity it is possible to calculatethe pressure coefficients kPe, kPi and kPr1 which are expressedaccording to the following relations:

kPe=(Pe−Ps _(∞))/(Pt−Ps _(∞))  (8)

or else:

kPe=1−(V 1 cos α+V 2 sin α)²(since Φ=0)  (9)

kPi=(Pi−Ps _(∞))/(Pt−Ps _(∞))  (10)

or else:

kPi=1−(V 1 cos α−V 2 sin α)²(since Φ=π)  (11)

kPr 1=(Pr 1−Ps _(∞))/(Pt−Ps _(∞))  (12)

or else:

kPr 1=1−(V′1 cos α)²−0.5(V′2 sin α)²−0.5(V′3 sin α)²  (13)

The coefficient kpr1 is calculated by averaging the coefficients of theeight intercommunicating holes forming the tap PPr1.

The components V′1, V′2 and V′3 of the velocity of the fluid flow at thepressure tap PPr1 are different from the components V1, V2 and V3 of thevelocity of the flow at the pressure taps PPe and PPi. This is becausethe pressure tap PPr1 is situated at a different abscissa from that ofthe pressure taps PPe and PPi.

The pressure coefficients kPe, kPi and kPr1 are periodic functions ofthe angle of attack α and they are of period π on account of the powerof two which comes into relations (9), (11) and (13).

The three pressure sensors C1, C2, C3 are associated with the pressuretaps. C1 is a differential sensor which measures P1=Pe−Pr1. C2 is adifferential sensor which measures P2=Pi−Pr1. C3 is an absolute sensorwhich measures P3=Pr1. A different choice may be made for the type(differential/absolute) of sensors.

The calculation means make it possible to calculate the ratio:

(P 1−P 2)/(P 1+P 2)

which is expressed according to the relations:

(P 1−P 2)/(P 1+P 2)=(Pe−Pi)/(Pe+Pi−2.Pr 1) or else:  (14)

(P 1−P 2)/(P 1+P 2)=(kPe−kPi)/(kPe+kPi−2.kPr 1)  (15)

In view of the expressions for kPe, kPi and kPr1 as a function of α, theratio (P1−P2)/(P1+P2) can be written in the form:

(P 1−P 2)/(P 1+P 2)=(a. sin(2α))/(b+c. cos(2α))  (16)

where a, b and c are constants which depend only on the position of thepressure taps on the probe.

By knowing the ratio (P1−P2)/(P1+P2) it is therefore possible tocalculate the angle of attack α. However, relation (16) generallycorresponds to a nonlinear function of the angle of attack α as afunction of the pressure ratio. For a limited range of angle of attack,this function may be rendered linear by virtue of a judicious choice ofthe constants a, b and c; that is to say, by virtue of a judiciouschoice of the position on the probe of the pressure taps. Such a choicemakes it possible for example to obtain:

a mean nonlinearity (square error) of ±10⁻³ over a range of angle ofattack of ±40° when c/b=0.560825,

or else a mean nonlinearity (square error) of ±3×10⁻³ over a range ofangle of attack of ±50° when c/b=0.59998,

or else a mean nonlinearity (square error) of ±7.5×10⁻³ over a range ofangle of attack of ±60° when c/b=0.65422.

The angle of attack being a quasi linear function of the pressure ratio,it can be calculated with good accuracy. The following numericalapplication illustrates a particular embodiment of the invention; theassumptions of the application are as follows:

the flight domain of the aircraft extends from 0 to 257 m/s, thiscorresponding to 500 kt in the measurement system commonly used inaeronautics,

the domain of angle of attack of the air stream is ±40° over thevelocity interval lying between 0 and 103 m/s, this corresponding to 200kt in the measurement system commonly used in aeronautics, and itdecreases with V² over the velocity interval lying between 103 and 257m/s, this corresponding respectively to 200 and 500 kt in themeasurement system commonly used in aeronautics.

The sensors C1 and C2 have to operate over the interval which extendsfrom −32 to +350 hPa. Taking as another constraint the fact that thesensors C1 and C2 have an accuracy of ±0.25 hPa, the calculation of theangle of attack α, for a velocity of 51 m/s, this corresponding to 100kt in the measurement system commonly used in aeronautics, is given withan accuracy of:

0.75° for α=±40°

0.5° for α=±30°

0.3° for α=+20°

0.25° for α=+0°

Knowing the angle of attack α, relations (9), (11) and (13) make itpossible to calculate the pressure coefficients kPe, kPi and kPr1.Relations (8), (10) and (12) can be combined so as to express thedynamic pressure (Pt−Ps_(∞)), the static pressure Ps_(∞) and the totalpressure Pt.

The dynamic pressure is given by the relation:

(Pt−Ps _(∞))=(P 1+P 2)/(kPe+kPi−2kPr 1)  (13)

The static pressure Ps_(∞) is given by the relation:

Ps _(∞) =P 3−kPr 1(Pt−Ps _(∞))  (14)

The total pressure is given by the relation:

Pt=(Pt−Ps _(∞))+Ps _(∞)  (15)

By replacing the pressure coefficients kPe, kPi and kPr1 in equations(13), (14) and (15) by their value, it is thereby possible to determinethe dynamic pressure, the static pressure Ps_(∞) and the total pressure.The pressures Pe and Pi are obtained by calculating P1+P3 and P2+P3respectively.

Taking a sensor C3 with a measurement swing of 0 to 1100 hPa, andaccuracy ±0.25 hPa, the accuracies in the values calculated for avelocity of 51 m/s, this corresponding to 100 kt in the measurementsystem commonly used in aeronautics, become:

for the calculated dynamic pressure

0.18 hPa for α=0°

0.28 hPa for α=±40°

for the calculated static pressure Ps_(∞)

0.14 hPa for α=0°

0.25 hba for α=±40°

FIG. 5 schematically represents, in a diagram, a particular arrangementof the pressure taps of the second embodiment of a probe according tothe invention. The probe comprises, in addition to the pressure tapsalready described in the first embodiment, a fourth pressure tap PPr2associated with the pressure measurement means. In the example adopted,the pressure measurement means comprise a fourth pressure sensor C4. Thefourth sensor C4 is chosen to be the same type as the third sensor C3.

The pressure tap PPr2 comprises, like the tap PPr1, a ring ofintercommunicating holes situated in one and the same section 9. Theholes of the tap PPr2 are situated at a different abscissa from that ofthe holes of the tap PPr1. The abscissa of the holes of the tap PPr2 ischosen in such a way that the pressure coefficient kPr2 is as differentas possible from the pressure coefficient kPr1 for the useful range ofangle of attack. The data provided by the sensor C4 make it possible toperform monitoring of the validity of the information. This monitoringis carried out as follows:

a first value of α, of (Pt−Ps_(∞)) and of Ps_(∞), as well as the valueof the pressures Pe and Pi are calculated, as described above, from theinformation provided by the sensors C1, C2 and C3.

a second value of α, of (Pt−Ps_(∞)) and of (Ps∞) are calculated, fromthe calculated values of Pe and Pi and, from the pressure measured bythe sensor C4. These second values are compared with the first values ofα, of (Pt−Ps_(∞)) and of Ps_(∞).

The result of the comparison makes it possible to detect a malfunctionin one of the measurement pathways.

In the case where the probe comprises four pressure taps in the firstsection, the two additional taps make it possible to calculate thesideslip of the air flow. This calculation is performed in a similarmanner to the calculation of the angle of attack α.

The multifunction probe described above makes it possible to determinethe velocity and angle of attack of the air flow on the basis of severalpressure taps.

It is known moreover that the actual velocity of the airplane depends onthe static temperature Ts of the air flow. This temperature beingdifficult to measure, the total temperature Tt of the air flow iscustomarily measured, from which the static temperature Ts is deductedthrough the following equation:

Tt=(1+0.2 M ²)Ts

Where M represents the Mach number. The Mach number is the ratio of thevelocity of the airplane to the velocity of sound. Now, the velocity ofsound Vs is dependent on the static temperature Ts of the air flow:

Vs={square root over (γ.r.Ts)}

in which equation:

γ is a constant equal to around 1.4

r is the ideal gas constant.

The Mach number is for its part calculated from the static pressure Ps-and from the total pressure Pt which were determined above:$M = \sqrt{5\left\lbrack {\left( \frac{Pt}{{Ps}\quad \infty} \right)^{2/7} - 1} \right\rbrack}$

Thus, the actual velocity of the airplane can be determined from thetotal pressure Pt, from the static pressure Ps_(∞) and from the totaltemperature Tt.

Separate probes are customarily made, one probe comprising the pressuretaps and another comprising means for measuring the total temperatureTt.

In accordance with the invention, by making a multifunction probe withno Pitot tap, it is advantageous to supplement it with means formeasuring the total temperature Tt. An example of such a probe isdescribed by means of FIG. 6.

In this figure, the multifunction probe comprises the body 1 connectedto a base 8 offset from the axis X and the function of which is tomaintain the position of the body 1 with respect to a skin 9 of theairplane. To simplify the figure, the pressure taps PPr1, PPr2 and PPeare not represented.

The multifunction probe furthermore comprises means for measuring thetotal temperature of the air flow.

Advantageously, these means comprise two channels, including a firstchannel 10 comprising an inlet orifice 11 substantially facing the airflow when the latter is oriented along the X axis. The first channel 10also comprises an outlet orifice 12 allowing air located in the firstchannel 10 to escape along the direction of the X axis. Any particleswhich may circulate through the first channel 10 escape without cominginto contact with a temperature sensor whose position will be describedlater. These particles are for example formed of droplets of water ordust.

The second channel 13 comprising means for measuring the totaltemperature of the air flow includes an inlet orifice 14 opening outinto the first channel 10. The second channel 13 is for examplesubstantially perpendicular to the first channel 10. Part of the aircirculating through the first channel 10 enters the second channel 13via the inlet orifice 14 and escapes from the second channel 13 via anoutlet orifice 15 opening to the outside toward the rear of the base 8.

The means for measuring the total temperature of the air flowfurthermore comprise a temperature sensor 16 situated inside the secondchannel 13. The temperature sensor 16 comprises for example a coiledplatinum-based wire forming an electrical resistor whose value can varyas a function of its temperature. The temperature is sensor 16 is fixedin the second channel 13 so as to avoid, to the greatest possibleextent, any heat transfer between the structure of the second channel 13and the temperature sensor 16.

The two channels 10 and 13 are contrived in such a way that the airoriginating from the air flow circulates through the second channel 13at low velocity. This velocity must be much less than the velocity ofsound in the flow while being non zero so as to prevent the temperaturesensor 16 from taking up the temperature of the structure of the base 8and in particular the temperature of the structure of the two channels10 and 13.

Specifically, when the aircraft is flying at high altitude, thetemperature of the air flow may be much less than zero degrees Celsius,this incurring a risk of ice formation on the multifunction probe. Theice may in particular obstruct these channels 10 and 13 and henceprevent any correct measurement of temperature.

To preclude the formation of ice, the moveable blade 1 comprisesde-icing means which include for example an electrical heating resistorarranged in the structure of the blade. These de-icing means heat up themultifunction probe and consequently the air circulating through the twochannels 10 and 13. To prevent the heating up of the air from disturbingthe temperature measurement, there are provided orifices 17 for removingthe boundary layer of the air circulating through the two channels 10and 13.

What is claimed is:
 1. A fixed multifunction probe for aircraft formeasuring flow parameters of fluid flowing with respect to the probe,comprising: a body having symmetry of revolution about a longitudinalaxis, closed by a rounded cap, the body being placed in the fluid flow,at least three pressure taps situated at specified positions of the bodyand distributed in plural sections so as to tap at least a firstpressure, a second pressure, and a third pressure, pressure measurementmeans associated with the pressure taps for measuring at least as manypressures as pressure taps, calculation means for calculating a localangle of attack α of the fluid flow by expressing a specified ratio ofmeasured pressures as a function of the local angle of attack α in aform:$\frac{{P1} - {P2}}{{P1} + {P2}} = \frac{A + {{B \cdot \cos}\quad 2\quad \alpha} + {{C \cdot \sin}\quad 2\quad \alpha}}{D + {{E \cdot \cos}\quad 2\quad \alpha} + {{F \cdot \sin}\quad 2\alpha}}$

 A, B, C, D, E, F being constants dependent solely on coordinates of thepressure taps, the specified positions of the pressure taps being suchthat the specified ratio as a function of the local angle of attack α isquasi linear, and the calculation means for calculating a total pressurePt of the fluid flow at a level of the probe, a static pressure atupstream infinity of the probe Ps_(∞), and dynamic pressure Pt−Ps_(∞)from pressure coefficients kP of the pressure taps.
 2. The fixedmultifunction probe as claimed in claim 1, wherein each section isperpendicular to the longitudinal axis of the body of the probe.
 3. Thefixed multifunction probe as claimed in claim 2, wherein the threepressure taps are distributed as: two pressure taps arranged in a firstsection and arranged in a plane of attack and diametrically opposite oneanother to tap the first pressure and the second pressure; a referencepressure tap arranged in a second section and including a ring ofregularly spaced holes intercommunicating to establish a first meanpressure.
 4. The fixed multifunction probe as claimed in claim 3,further comprising: a fourth pressure tap arranged in a third section,separate from the first and the second sections, and including a ring ofregularly spaced holes intercommunicating to establish a second meanpressure, and wherein the calculation means calculates a second value ofthe local angle of attack α, of the dynamic pressure Pt−Ps_(∞) and ofthe static pressure Ps_(∞) to validate the calculated values bycomparison.
 5. The fixed multifunction probe as claimed in claim 4,wherein the fourth pressure tap comprises eight holes separated from oneanother by an angle of 45°.
 6. The fixed multifunction probe as claimedin claim 3, wherein the pressure tap arranged in the second sectioncomprises eight holes separated from one another by an angle of 45°. 7.The fixed multifunction probe as claimed in claim 3, wherein thepressure measurement means measures a first differential pressureP1=Pe−Pr1 and a second differential pressure P2=Pi−Pr1 between the firstand the second sections, and an absolute pressure P3−Pr1 at a level ofthe reference tap.
 8. The fixed multifunction probe as claimed in claim7, wherein the calculation means calculates the flow parameters from therelations: (P 1−P 2)/(P 1+P 2)=(α·sin(2α)/(b+c·cos(2α)), in which a, b,and c are constants dependent solely on the positions of the pressuretaps on the probe, (Pt−P _(∞))=(P 1+P 2)/(kPe+kPi−2kPr 1), in whichkPe=1−(V1 cos α+V2 sin α)², kPi=1−(V1 cos α−V2 sin α)², kPr1=1−(V′1 cosα)²0.5(V′2 sin α)²−0.5(V′3 sin α)², and V1, V2, and V3 are components ofa velocity of the fluid flow at a level of the first section, and V′1,V′2, and V′3 are components of a velocity of the fluid flow at a levelof the second section, Ps _(∞) =P 3−kPr 1(Pt−Ps _(∞)), and Pt=(Pt−Ps_(∞))+Ps _(∞).
 9. The fixed multifunction probe as claimed in claim 1,further comprising means for measuring a total temperature of an airflow as the fluid flow.
 10. The probe as claimed in claim 9, wherein themeans for measuring the total temperature comprises: a first channelcomprising an air inlet orifice substantially facing the air flow and anair outlet orifice; a second channel whose air inlet is situated in thefirst channel; and a temperature sensor fixed in the second channel. 11.The probe as claimed in claim 10, wherein the two channels comprise aplurality of orifices configured to remove toward the outside of theprobe, the boundary layer of the air circulating through the channels.